The compromise package would spend $940 billion to extend coverage to 32 million Americans over the next decade, leaving only about 5 percent of non-elderly citizens without coverage, according to projections by the nonpartisanCongressional Budget Office. Millions of people would be added to the rolls of Medicaid, the government health program for the poor, while millions more who lack access to affordable coverage through the workplace would receive federal tax credits to buy insurance.

For the first time, every American would be required to obtain coverage or face a penalty of at least $695 a year. Employers, too, would have a new responsibility: to offer coverage or face penalties of $2,000 per worker. By cutting more than $500 billion from Medicare over the next decade and raising taxes on the well-insured and high-earners, the package would trim deficits by $138 billion over the next decade and by around $1.2 trillion in the decade thereafter, the CBO said.

Republicans questioned assertions of deficit-reduction, predicting that Democrats would abandon the measure's primary funding mechanisms when seniors begin to feel the pinch of Medicare cuts, or when union families fall victim to a new 40 percent tax on the most generous insurance policies set to take effect in 2018. If those and other politically painful provisions were removed, the CBO said, the measure would increase deficits.

"This is going to be a program that will rival the size and liability of Medicare for sure, in my opinion," said Rep. Paul Ryan (R-Wis.).

The Republican message was being received loud and clear outside the Capitol, where angry protesters gathered and waved placards that said "Defeat Obamacare" and "Born in the USA not the USSR." Republicans were treated as heroes as they walked through the crowds, who patted them on the back and thanked them for their opposition. Democrats were greeted with jeers.

Black lawmakers said some protesters hurled racial epithets at them, and in one instance, spit upon them.

Rep. Emanuel Cleaver (D-Mo.) said that he was walking into the Capitol to vote when a protester spat on him. Police quickly responded and detained the protester, Cleaver said in a statement, but the lawmaker declined to press charges.

"They were shouting the N-word," Carson told reporters. "It was like a page out of a time machine."

Observers also said that Rep. Barney Frank (D-Mass.) was heckled with anti-gay epithets inside the Longworth House Office Building.

"I have heard things today that I have not heard since March 15, 1960, when I was marching to get off the back of the bus," said House Majority Whip James E. Clyburn (D-S.C.), the highest-ranking black official in Congress.